Current flow timing device



Jan. 18, 1938... D. c. WRIGHT ,1

CURRENT mow TIMING DEVICE "Filed April 2'7, 193$ 3 Sheets-Sheet l I IvEgvToR I v BY 2 J 1 MTTORNEY Jan. l8 193s.

D. c. WRIGHT 2,105,899

CURRENT FLOW TIMING DEVICE Filed April 27, 1935 s Sheets-Sheet 2 Jan.is, 1938.

D. C. WRIGHT CURRENT FLOW TIMING DEVICE Filed April 27, 1935 sSheets-Sheet s v ix.

Patented Jan. 18, 1938 -;PArENr--orr1cs cunnsn'r rnow TIMING (DEVICEDavid C. Wright, Euclid, Ohio, assignonsto The. Electric Controller &Manufacturing ('Jo'mpanyr Cleveland, Ohio, a corporation of OhioApplication April 27, 1935; Serial No. 18,490

27 Claims.

This invention relates to apparatus for timing the duration ofapplication of electric current to a workwcircuit, and for timing theduration of the period between successive applications of electriccurrent to the work-circuit, and an object of the invention is toprovide a new and improved apparatus of this character.

Another object is to provide improved means to automatically time theduration of current flow in a work-circuit for durations of timesubstantially inversely proportional to the strength of the current inthe work-circuit, whereby the duration of current flow in thework-circuit is automatically varied and a substantially predeterminedquantity of current is supplied to the work-circuit regardless of theresistance of the work-circuit.

Another object is to'provide means to automatically determine theduration of current flow 20 in a work-circuit for durations of timesubstantially inversely proportional to the magnitude of the voltageapplied to the workcircuit, whereby the duration of current flow in thework-circuit is automatically varied dependent upon the mag- 25 nitudeof the voltage applied to the work-circuit.

A further object is to provide means to automatically time the durationof the period between successive applications of electric current to awork-circuit for durations of time substantially 30 inverselyproportional to thestrength of the voltage applied to said means.

Other objects will appear as my invention is described hereinafter.

This application is a continuation in part of ..5 my co-pendingapplications serial Nos. 629,642 and 629,643, filed August 20, 1932,since matured into Patent Nos. 2,023,631 and 2,024,019, dated Dec. 10,1935 and Serial No. 737,419, filed July 28, 11934. 40 In the drawingsaccompanying this specificati0n-and formingpart ofthis application Ihave shown, for purposes of illustration, certain embcdiments which myinvention may assume, and in these drawings: 45 Figure 1 is a circuitdiagram of one embodiment of my invention,

Figure 2 is a circuit diagram of another embcdiment of my invention, andH Figure 3 is another circuit diagram of a different embodiment of myinvention.

The embodiment ofthe invention disclosed in Fig. 1 includes a schematicarrangement of parts of a spot-welding machine, not completely shown,

ctmprising a cylinder 5, a pressure switch 6, an.

55 inlet fluid conduit 1, and outlet fluid conduit 8, a

control valve 9 which-controls the flow of fluid in the conduits 1 and},a movable electrode l9 and a stationary electrode 20. The movableelectrode l9 ismoved by the fluid in the cylinder 5 into engagement witha work-piece-2l and presses the 5 latter against a work-piece 22, hereshown in engagement with the stationary electrode 20. The pressureswitch 6 is adapted to be closed after the movable electrode I9 is inengagement with the workpiece 2i and after ,a predetermined pressure hasbeen developed in'the cylinder 5.

Included in the work-circuit is a welding transformer l0 provided with aprimary winding ll supplied with alternating current from a pair ofsupply lines 12 arid l3 through conductors I1 15 and I3 in which isinterposed a magneticallyoperated welding switch It normally held inopen position by a. spring l5. The secondary winding N5 of the weldingtransformer I0 is adapted to be connected to the welding electrodes l9and 20. n

The control 'valve 9 is "provided with an operating coil 23 having oneterminal connected through a conductor 24 to the supply line I3 and theother terminal connected through a conductor 25 to a movable contact arm26 of a relay 21. 25

The relay 21 is provided with a relatively stationary contact 36connected through conductors 31 and 3| to the supply line l2, and isfurther provided with an operating coil 23 having one of its terminalsconnected through a conductor 29 to the supply line l3, and having theother of'its terminals connected through a conductor 33, normally closedcontacts. of a control relay 35, and a conductor 32 to anotherrelatively stationary contact 33 of the control re- 35 lay 21.v

Connecting the conductors 3| and 32 is a push button 30 closure of whichenergizes the operating coil 28' of the relay 21 to move the contact 26into engagement with the contacts 38 and 36. 0

Closure of the contacts 36 and 26 ofthe relay 21 completes theenergizing circuit for the operating coil 23 of the valve 9.

Engagement of the contacts 36, 38 and 26 of the relay 21 completes aholding circuit for maintaining the operating coil-28 of the. relay 21energized in case the push-button 30 is released during a weldingperiod.

The welding switch I is provided with an operating coil 39 which has oneterminal con- 50 nected to aconductor 40 and in turn connected to thesupply line l3, and has another terminal connected to a conductor 4!,pressure switch '6, conductors I and 25, contacts 26 and 36 of the.relay 21, and the conductors 31 and 3| to the 55 supply line I2.Closure of the pressure switch 8 effects energization of the operatingcoil 38 which then closes the switch I4.

The duration of time that the welding switch I4 is maintained closed maybe controlled by means hereinafter identified as on timing means for thereason that they determine the duration of the on period, that is, thewelding period, and comprise in this instance, a series transformer 43having its primary winding 44 interposed in circuit with the circuit ofthe primary winding II of the welding transformer I8.

A rectifier 45 is provided for rectifying the alternating currentsupplied by the secondary winding 46 of the series transformer 43. Thesecondary winding 46 and the rectifier 45 are respectively connected tooutput conductors 41 and 48, the conductor 41 being connected to acenter tap 58 of the secondary winding 48, and the conductor 48 beingconnected to one of the electrodes 48 of the rectifier 45. The rectifier45 also has electrodes 58 and 5| connected respectively to the terminals52 and 53 of the secondary winding 4I5. Shunted across the electrodes 58and 5| of the rectifier 45 is a variable resistance 68, which can beopen-circuited if desired.

The output conductors 41 and 48 are adapted to supply unidirectionalcurrent to the operating coil of a sensitive relay 54, here shownconnected in series with a neon tube 55. A condenser 56 has itsterminals connected to. the output conductors 41 and 48 inshunt' withthe sensitive relay 54 and theneon tube 55. Also' .ductor 48, is anadjustable'resistance 58 disposed on the supply side of the condenser58.

The operating coil of the sensitive relay 54 is here shown as having aconductor 66 tapped thereto at a point 65 intermediate the terminals ofthe operating coil of the sensitive relay 54. The conductor 66 isconnected through the normally-open contacts 81 of the control relay 35and a conductor 68 to the output conductor 41.

The sensitive relay 54 is provided with relatively stationary contactsBI and 62, and a movable contact arm 63 which normally engages thestationary contact 62. The stationary contact 8| being connected througha conductor 54 and the conductor 3| tothe supply line I2.

The operating coil 89 of the control relay 35 has one of its terminalsconnected through a conductor 18 to the movable contact arm 63 of thesensitive relay 54, and has the other of its terminals connected toaconductor 1|, normally-closed contacts 12 of ja control relay 13, aconductor 14, and the conductor 28 to the sup-'- ply line I3. Connectedto the conductors 32 and 18 are normally-open contacts 15 f the controlrelay 35.

The duration of time that the welding switch I4 is maintained open maybe controlled by means hereinafter identified as off timing means forthe reason that such means determine the duration of. the oil period,that is,

the period between successive welding periods,

- and comprise in this instance an auto transformer .16 provided withterminal taps 11 and 18, a center tap 18, and intermediate taps 88 and8|.

A rectifier 84 is provided for rectifying the alternating currentsupplied by the auto trans former 16, and the rectifier 84 haselectrodes 85 and 86 connected respectively to the terminal taps 11. and18 of the auto transformer'15. An output conductor 81 is connected tothe center tap 18 of the transformer winding, and an output conductor 88is connected to another one of the electrodes 88 of the rectifier 84.

The output conductors 81 and 88 are adapted to supply unidirectionalcurrent to the operating coil of a sensitive relay 88 here shown asconnected in series with a neon tube 8|. A condenser I85 has itsterminals connected to the output conductors 81 and 88 in shunt with thesensitive relay 88 and the neon tube 8|. Also shunted across the outputconductors 81 and 88 is a resistance 82. Interposed in one of the outputconductors, here shown as output conductor 88, is an adjustableresistance 83 disposed on the supply side of the condenser I85.

The operating coil of the sensitive relay 88 is here shown as having aconductor 88 tapped thereto at a point 88 intermediate as between theterminals of the operating coil of the sensitive relay 88. Theconductor: 88 is connected through the normally-open contacts I88 ofvthe control relay 13 and a conductor IN to the output conductor 81.

The sensitive relay 88 is provided with a relatively stationary contact85 and a movable contact arm 88 which is connected through conductors81, 64, 3| and to the supply line I2. The operating coil I82 of thecontrol relay 13 has one of its terminals connected to one of thecontacts 12 of the-control relay 13 and has the other of its terminalsconnected through a conductor I83 to the stationary contact 85 of thesensitive relay 88.

Interposed in the conductor 82 is a selector switch I84 which is adaptedto open or to close the circuit between the conductor 1| and theintermediate terminal 88 of the transformer 15'. When the selectorswitch I84 is in closed position the system is adapted to providealternate repeat operations of the on timing means and of the of! timingmeans, and when in open position is adapted to permit only operations ofthe "on timing means.

In operation, assume it is desired to have repeat operation, that isalternate operation of the on time circuits and of the off timecircuits, the selector switch I84 is placed in repeat position whichcloses the, conductor 82.

The push-button 38 is closed to complete the energizing circuit for theoperating coil 28 of the relay 21, from the supply line I2 throughconductor 3|, push-button 38, conductor 32, normally closed contacts 34of. the control relay 35,

conductor 33, operating coil 28, and conductor 28 to the supply line I3.Energization of the operating coil 28 eiiects closing of the contact arm25 which completes'the energizing circuit for the operating coil 23 ofthe valve 8, from the supply line I2, through conductors 3| and 31,contacts 38 and 25, conductor 25, operating coil 23 and conductor 24 tothe supply line I3. Energization of the operating coil 23 operates thecontrol valve 8 to open the inlet conduit 1 and to close the outletconduit 8 whereby fluid enters the cylinder and moves the' electrode I8into engagement with the work-piece 2|,

Upon engagement of the electrodes I8, and 28 with the work-pieces 2|.and 22 and after a pre-' determined pressure is exerted bythe'electrodes 'I8 and 28'onthe work-pieces 2| and 22, the pressureswitch 5 is automatically closed by thefluid in the cylinder 5. Closureof thepressure switch 6 completes the energizing circuit for the operthesupply line I2, conductors ating coil 39 of the switch I4,'fro m thesupply line I2 through conductors 3| and 31,- contacts 36 and 26,conductors 25 and 4, pressure switch 6, conductor 4|, operating coil 39,and conductor 40 to the supply line I3. V The energized operating coil39 closes the switch I4 to permit flow of current. through the primarywindings .44 and II tothe work-pieces 2| and, 22 to start a weldingperiod.

A voltage is induced in the secondary winding 46 from the primarywinding 44. The voltage delivered by the secondary winding 46 isrectified by the rectifier 45 which provides unidirectional voltage tothe condenser 56. The condenser 56 accumulates a charge until apredetermined voltage is reached, at which voltage the and 29 to thesupply line I3. Energization o! the neon tube 55 becomes conducting andpermits discharge of .the charge accumulated in the condenser 56.

The sensitive relay 54 isenergized when the neon tube 55 becomesconducting and is maintained energized for a' period, moving the contactarm 63 into engagement with the contact 6|. Closure of the contacts 6|and 63 of the sensitive relay 54 completes an energizing circuit for theoperating coil 69 of the control relay 35, from 3| and 64, contacts 6|and 63, conductors 10, operating coil 69, conductor 1|, normally closedcontacts 12 of the control relay 13, and conductors 14 and 29 to thesupply line I3.

Energization of the operating coil 69 of the control relay 35 opens thecontacts 34 and closes the contacts 61 and 15 of the control relay 35.

Opening of the contacts 34 of the control relay 35 de-energizes theoperating coil 28 of the relay 21, which then de-cnergizes the operatingcoil 23 of the control valve 9 and the operating coil 39 of the weldingswitch I4, interrupting the flow of current to the work-pieces natingthe welding period.

The closing of the contacts 61 of the control relay 35 completes a shuntcircuit from the output conductor 48, through a portion of the operatingcoil of the sensitive relay 54, the conductor 66, through the closedcontacts 61 and the conductor 68 to the output conductor 41. Thecondenser 56 discharges through this shunt circuit and maintains thetapped portion of the operating coil of the sensitive relay 54 asincluded in the shunt circuit, energized for a suflicient length of timeto maintain the sensitive relay contacts 6| and 63 closed for a periodafter the closureof the contacts 15 of the control relay-35.

Closing of the contacts 15. maintains the control relay 35 energized,which wouldotherwise be de-energized by the opening of the contact 6| ofthe sensitive relay 54. After closure of the holding circuit contacts15, the discharge from the condenser 56 is not sufficient to maintainthe tapped portion of the sensitive relay 54 sufl'iciently energized tohold the contact 63 in engagement with contact 6|, and accordinglycontact 6| opens, and the contacts 63 and 62 close whichcompl'te anenergizing circuit for the auto-transformer 16, from the supply line I2,through conductor 3|, push-button 30, conductor 32, closed contacts 15,conductor 10, contacts 63 and 62, conductor 83, transformer 16.conductor 62. closed selector switch I04, conductor 1|, closed. contacts12 of the control relay 13, conductor 14, and conductor 29 to the supplyline I3.

The voltage delivered by the auto 16 is rectified by the rectifier 84which provides unidirectional voltage to the condenser I05. The

2| and22, andterrnitransformer- 'pletes an energizing circuit for theoperating coil I02 of the control relay 13 from the supply line I2,through the conductors 3|,64 and 91, contact arm 96, contact 95,conductor I03, operating coil I02 of the control relay 13, andconductors 14 operating coil I02 of the control relay 13 opens thecontacts 12 and closes the contacts I00.

Opening of the contacts 12 de-energizes the operating coil 69 of thecontrol relay 35 which opens the holding circuit contacts 15, and closesthe contacts 34, thus completing the circuit to 'the'operating coil 28of the relay,21 to thereby begin another welding period. Opening of thecontacts 12 also interrupts flow of current to the auto-transformer 16.

At the same time the closing of the contacts I00 of the control relay 13completes a shunt circuit from the output conductor 88, through aportion of the operating coil of the sensitive relay .90, the conductor99, through the closed contacts I00 and the conductor I0l tor 81.

The condenser I05 discharges through the foreto the output conducgoingshunt circuit and maintains the tapped.

portion of the operating coil of the sensitive relay 90, included in theshunt circuit, energized for a sufficient length of time to hold thesensitive relay contacts 95 and 96 closed fora period after opening ofthe contacts 12 of the control relay 13. Maintaining the sensitive relaycontacts 95 and 96 closed for a period insures sufiicientde-energization of the operating coil 69 of thecontrol relay 35 todefinitely open the contacts 15 and to definitely close the contacts 34.After definite closure of the contacts 34,

the discharge from the condenser I05 is not suflicient to maintain thetapped portion of the sensitive relay sufficiently energized to hold thecontacts and 96 closed, and accordingly contacts 95 and 96 open,breaking the circuit to the operating coil I02 of the control relay 13,which then operates'to close the contacts 12. Closure of the contacts 12of the control relay I02, and of the contacts 34 of the control relay 35places the on-timing means again in circuit for another welding period.

' I Alternate repeat operations of the on timing means and of the ofitiming means is obtained as long as the push-button 30 is held closed.If the push-button 30 is opened while a weld is in progress the weldingoperation will continue until the weld is completed, and the alternaterepeat operations of the on timing means and of the oil timing" meanswill then cease, but may be started by again-closing the push-button.

For single welds, that is performing welds without employing-the of!timing means, the selector switch I04 is moved to its single position,which is its open position, and prevents operation ofthe'auto-transformer 16. On repeatedoperation of the push-button 30,single repeat welding operations of the on timing means will be hadwithout operation of the off timing means.

From the foregoing, it will be perceived that the magnitude of thevoltage supplied to the secondary winding 46 of the transformer 43 is afunction of the magnitude of the current flowing through the work-pieces2| and 22. Consequently, the time required for the condenser 56 toaccumulate a sufficient charge to permit the neon tube circuit to becomeconducting and energize the sensitive relay 54, is greater for smallcurrents passing through the work-pieces 2| and 22, and is less forlarge currents passing through the work-pieces 2I and 22. v

In other words, the duration of the welding period is not constant butis automatically determined and varied by the magnitude of the currentflowing through the work-pieces 2I and 22. Accordingly, my invention isadapted to weld together work-pieces of different thicknesses, or ofdifferent material, since the on timing means willautomatically-interrupt the flow of current to the work-pieces after apredetermined quantity of current has passed through the workpieces tothereby uniformly weld all of the workpieces.

The duration of the welding period may be varied by varying theresistance 59, thereby increasing or decreasing the resistance in thesupply circuit of the condenser 56 and decreasing or increasing thecharging rate of the condenser 56 thus lengthening or shortening thewelding period.

The welding period may also be varied by varying the capacity of thecondenser 56, and the number of or characteristics of the neon tube 55.7

The current range of the transformer 43 is changed by varying theloading resistance 60. Increasing the resistance 60 increases themagnitude of the voltage in the secondary winding 46 and the voltagesupplied to the'condenser 56; causing the condenser 56 to more rapidlyaccumulate the voltage required to operate the neon tube 55, anddecrease the duration of operation of the on timing means and theduration of current flow in the work-circuit.

It will also be perceived that the duration of the off period", that isthe period between successive welding periods, is substantiallyconstant, and is dependent upon the magnitude of the voltage supplied toand furnished by the auto transformer 16. The duration of the offperiod." may be altered by varying the resistance 93, by varying thecapacity of the condenser I05 and by varying the number of orcharacteristics of the neon tube 9i.

Referring to Fig. 2; the embodiment of the invention therein disclosedcomprises a load H0 adapted to be supplied with alternating current froma pair of supply lines H2 and H3, through conductors H4 and H5 connectedrespectively to electrodes H6 and H1 here shown respectively in anengagement with the load H0.

Interposed in the conductors H4 and H5 is a magnetically operated switchH8 normally held in open position by means of a spring H9. Theswitch H8is closed upon energization of its operating coil I20 having one of itsterminals connected to a conductor I 2I in turn connected to the supplyline H3, and having the other of its terminals connected to a conductorI22, normally-closed contacts I23 of a control relay I24, conductors I25 and I26 to the supply line H2. The operating coil I20 of the switchII 8 isenergized by the closure of a push-button I21 interposed in theconductor I26.

tube I45.

The duration of time that the switch m is maintained closed may becontrolled by means herein identified as "on timing" means for thereason that they determine the duration of the on period, that is, theperiod that current is supplied to'the load H0, and comprise in thisinstance, an auto transformer I28, having its winding I29 provided withterminal taps I30 and I3I, a center tap I32 and intermediate taps I33and I34. Alternating current is supplied to the winding I29 from thesupply line II 2' through i the conductor I26, a conductor I35, windingI29, a conductor I36 and the conductor I2'I connected to the supply lineI I3.

A rectifier I31 is provided for rectifying the alternating currentfurnished by the auto-transformer I28, and has electrodes I38 and I39connected to the terminal taps I30 and I3I respectively of the windingI29 of the transformer I20.

An output conductor I40 is connected to another electrode I4I of therectifier I31; and an output conductor I42 is connected to the centertap I32 of the winding I29 of thetransformer I28. The output conductorsI40 and I42 are adapted to supply unidirectional current to theoperating coil I43 of a sensitive relay I44, here shown connected inseries with a neon tube I45.

A condenser I46 has its terminals connected to the output conductors I40and I42 in shunt with the sensitive relay coil I43 and the neon Shuntedacross the output conductors I40 and l42 isia'resistanee I48.

interposed in the output conductor I40 is a variable resistance I41 andnormally open contacts I49 of a relay I50. Energization of the operatingcoil I5I of the relay I50 effects closure of the normally open contactsI49 to complete the circuit to the condenser I46. The operating coil I5Ihas one'of its terminals connected to a conductor I52 in turn connectedto conductor I22, and has the other of its terminals connected to aconductor I53 in turn to a conductor I54 which is connected to thesupply line H3.

The operating coil I43 of the sensitive relay I44 is here shown ashaving a conductor I56 tapped thereto at a point I55 intermediate theterminals of the operating coil I43. The conductor I56 is connectedthrough the normally open contacts I51 of the control relay I24, aconductor I56, and a conductor I59 to the output conductor I42.

The sensitive relay I44 is provided with a relatively stationary contactI60 and a movable contact arm I6I which is connected to a conductor I62in turn connected through the conductor I26 to the supply line I I2.

The operating coil I65 of the control relay I24 has one ofits terminalsconnected through one of the normally open contacts I64 of the controlrelay I24 to a conductor I63 to the stationary contact I60 of thesensitive relay I44, and

it has the other terminal connected to a conductor I66, normally closedcontacts I 61 of a reset relay I68 and a conductor I69 to the conductorI54 in turn connected to the supply line H3.

The duration of time that the switch H6 is maintained open may becontrolled by means hereinafter identified as 'off timing means becausesuch means determine the duration of the off period, that is, the periodbetween successive applications of,current to the load H0, and comprisein this instance an output conductor I10 connected to the rectifier I31through conductor I40. The output conductors I42 and I10 supplyunidirectional current to the operating 15,1os,soa

coil I ll of a sensitive relay I12 here shown connectod in series with aneon tube I13.

A condenser I16 has its termi connected to theoutput conductors I10 andI42 in shunt with the sensitive relay coil Ill and the neon tube I13.'The'resistance I48 is also shunted across the output conductorsI42'and-110.

interposed in the output conductor I10 is a variable resistance I16 andthe normally closed contacts I11 of the relay I60, which controls thecircuit to the-condenser I15, the neon tube I13 and the sensitive relayI12.

A selector switch I86 interposed in the output conductor I10 is adaptedto open or to close the output conductor I18 and thereby respectivelyopen or close the circuit between the transformer I28 and the condenserI15 and neon tube I13. when the selector switch I86 is in closedposition the system is adapted to provide alternate repeat operations of.the ontiming. means and of the oil timing means, and when in openposition is adapted to provide only operations of the on timing means.

The operating coil I1I of the sensitive relay I12 is here shown ashaving a conductor I80 tapped thereto at a point I18 intermediate theterminals of the operating coil I1I of the sensitive relay I12. Theconductor I80 is connected,through thenormally open contacts I8I of thereset relay- I68 to the conductor I58 in turn connected to the outputconductor I42. 1

The sensitive relay I12 is provided with a relatively stationary contactI82 and a movable contact arm I83 which is connected through theconductor I62 to the conductor I26 to the supply line H2.

The operating coil I85 of the reset relay I68 has one of its terminalsconnected through'a conductor I84 to the stationary contact I82 oi thesensitive relay I12, and the other of its terminals is connected to theconductor I68.

In operation, assume it is desired to have repeat operation, that-isalternate operation of the .on time and off time circuit means, the

- selector switch I86 is disposed in its"repeat position, that is itsclosed position.

The push-button I21 is closed to complete an energizing circuit for theoperating coil I of the switch II8, from the supply line II2, throughconductor I26, push-button I21, conductor I25,

normally-closed contacts I23 of the control relay m, conductor m,operating coil I30, andthe conductor I2I- to the supply line I I3.Ener'gization of the operating coil I20 closes the switch I I8permitting current flow to the electrodes H6 and H1 and the applicationof the current to the load no.

Closure of the push-button I21 effects energi-' zation of the operatingcoil I6I of the relay I60 to close the contacts I48 and thus close theoutput conductor I40 and complete thecircuits to the condenser I46 andneon tube I46. Closure or the push-button I21 also completes a circuitto the auto transformer I28 whereby the latter is supplied with currentfrom the supply lines I I2- I and"I I3.

The voltage furnished by. the auto -transformer I28 is rectified,' bythe rectifier I31, providing unidirectional current to the condenserI48. The

condenser I46 accumulates a charge until apredetermined yoltage isreached, at which voltage the-neon tube l46'beoomes conducting andpermits discharge of the charge accumulated by the condenser I46. r s

The operating coil I43 of the sensitive relay I44 is energised when theneon tube I46 becomes conducting and is maintained energized for a shorttime to move the contact arm I6I into a engagement with the stationarycontact I60.

from the supply line II2, through conductor I26,

push-button I21, conductor I62, contacts I6I and I60, conductor I63,operating coil I65 of the control relay I24, conductor I66, contacts I61of the reset relay- I68 and conductors I68 and I54 to the supply line II3. Energization of the operating coil I65 of the control relay I24opens the contacts I23 and closes the contacts I64 and I51 of thecontrolrelay I24.

Opening of the contacts I23 de-energizes the operating coil I20 of theswitch II8, permitting the spring I I8 to open the switch I I8 whichinterrupts the flow of current to the electrodes H6 and H1 and to theload 0. Opening of the contacts I23 also de-energizes the operating coilI5I of the relay I50, which then opens its contacts I48 to interruptflow of current to the condenser I46, and closes its contacts "1' tocomplete the circuit of the output conductor I10 to the condenser I15.

,At the same time closure of the contacts I51 of the control relay I24completes a shunt circuit from the output conductor I40 through aportion of the operating coil I43 of the sensitive relay I40, theconductor. I56; contacts I51, and conductors I58 and I58 tothe outputconductor I42.

The condenser I46 discharges through the foregoing shunt circuit andmaintains the tapped portion of the operating coil I43, included in theshunt circuit; energized for a sufilcient length of time to hold thesensitive relay contacts I60 and I6I closed for a period after closureof the contacts I64 of the control relay I24. After definite closure ofthe contacts I64 the discharge from the condenser I46 is not sufllcientto maintain the tapped portion of the operating coil I43 sufllcient-I65, con uctor I66, contacts I61, conductor I68, and con uctor I54 tothe supply line H3.

The of! timing" means are arranged in circuit when the contacts I11 ofthe relay I50 are closed.

The voltage now furnished by the transformer I28 is rectified by therectifier I31 which provides unidirectional current to the condenserI16.. The condenser I16 accumulates a charge until a predeterminedvoltage is reached, at which voltagev the neon tube I18 becomesconducting and per- .mits discharge of the charge accumulated in thecondenser I15; 3

The operating coil "I of the sensitive relay I12 is-energlzed when theneon tube I13 becomes conducting .and is maintained energized for ashort timeto thereby move the contact arm I83- into engagement with thestationary contact I82. Closure of the contacts I82 and I83 of thesensitive relay I12 completes an energizing circuit for the supply lineII2 through conductor I28, pushthe operating coil I85 0! the reset relayI68 from 1 button I21, conductor I62, contacts I83 and I82 of thesensitive relay I12, conductor I84, operating coil I of the reset relayI68 and conductors I69 and I54 to the supply line II 3. Energization ofthe operating coil I 85 of the reset relay I68 opens the contacts I61and closes the contacts I8 I thereof.

Opening of the contacts I61 de-energizes the operating coil I65 of thecontrol relay I24, to open the holding contacts I64 and to close thecontacts I 23. Closure of the contacts I23 of the control relay I24effects energization of the operating coil I20 which closes the switchII8to again permit flow of current to the load IIII.

At the same time closing of the contacts I8I of the reset relay I68completes a shunt circuit from the output conductor I10 through aportion of the operating coil I1I of the sensitive relay I12, conductorI80, contacts NH, and conductor I59 to the output conductor I 42.

The condenser I 15 discharges through the foregoing shunt circuit andmaintains the tapped portion of the operating coil I1I, included in theshunt circuit, energized for a suflicient length of time to hold thesensitive relay contacts I82 and I83 closed for a short time afteropening of the contacts I61 of the reset relay I68. Maintaining thesensitive relay contacts I82 and I83 closed for this short time insuressufficient de-energization of the operating coil I65 of the controlrelay I24 to definitely open its contacts I64 and definitely close itscontacts I23.

After closure of the control relay contacts I23 the discharge from thecondenser I15 is too weak to hold the sensitive relay contacts I83 andI82 closed, and accordingly contacts I82 and I83 open to break thecircuit to the operating coil I85 of the reset relay Alternate repeatoperations of the on timing means and the off timing means is obtainedas long as the push button I21 is closed.

For single applications of current to the load IIO, the selector switchI86 is moved to its "single position, which is its open position, andprevents operation of the off timing means. Under these conditions thecondenser I15 and operating coil "I of the sensitive relay I12 willremain de-energized, and the contacts I82 and I83 of the sensitive relayI12 will remain open. On repeated operation of the push-button I21single welding operations of the on timing means will be had withoutoperation of the oil timing" means.

In this embodiment, as illustrated in Fig. 2; I

.have provided means to automatically control the duration of the onperiod that is the period during which current is supplied to the loadIIO, and7or to automatically control the duration of the off period thatis the period between successive on periods. The duration of the onperiod and of the off period is determined by the magnitude of thevoltage supplied to and furnished by the auto-transformer.

According 'ly increasing the magnitude of the voltage furadapted to'besupplied with alternating current.

from supply lines 202 and 203, through conductors 204 and 205 connectedrespectively to electrodes 206 and 201, here shown in engagement withthe load 200.

Interposed in the conductor 204 is the primary winding 2I9 of atransformer 220. Interposed in the conductors 204 and 205 is a controlswitch 208 held normally open by means of a spring 209. The switch 208is provided with an operating coil 2I0 having one of its terminalsconnected to a conductor 2 in turn connected to the supply line 203, andhaving the other of its terminals connected to a conductor 2I2, normallyclosed contacts 2I3'of a control relay 2I4, conductors 2I5 and 2I6 tothe supply line 202. Interposed in the conductor H6 is a push-button 2 I1, and closure of it effects energization of the operating coil 2I0,which then closes the switch 208.

The duration of time that the switch 208 remains closed may becontrolled by means herein identified as on timing" means, because theydetermine the duration of the -on period, that is, the period that thecurrent is supplied to the load 200, and comprise in this instance thetransformer 220 having its secondary winding 22I provided with terminaltaps 222 and 223, acenter tap 224 and intermediate taps 225 and 226, thelatter tap being connected through the conductor 2 to the supply line203.

A rectifier 221 rectifies the alternating current furnished by thetransformer 220 and has electrodes 228 and 229 connected respectively tothe terminal taps 222 and 223 of the transformer 220. Shunted across theelectrodes 228 and 229 of the rectifier 221 is a variable resistance 230which can be open-circuited if desired.

Connected to the center-tap 224 of the transformer 220 is an outputconductor 23I; and connected to another electrode 232 of the rectifier221 is an output conductor 233. The output conductors 23I and 233 areadapted to supply unidirectional current to the operating coil 234 ofasensitive relay 235, here shown connected in series with a neon tube236.

A condenser 231 has its terminals connected to the output conductors 23Iand 233 in shunt with the sensitive relay coil 234 and the neon tube236. Also shunted across the output conductors 23I and 233 is aresistance 238. 4

Interposed in the output conductor 233 is an adjustable resistance 239and normally open con tacts 240 of a relay 24I. Energization of theoperating coil 242 of the relay 24] effects closure of the normally opencontacts 240 to complete the circuit to the condenser 231 and thesensitive relay 235. The operating coil 242 of the relay 24I has one ofits terminals connected to a conductor 243 in turn connected to theconductor 2I2, and has the other of its terminals connected to aconductor 244 in turn connected to a conductor 245 which is' connectedto the supply line 203.

The operating coil 234 of the sensitive relay 235 is here shown ashaving a conductor 246 tapped thereto at a point 241 intermediate theterminals of the operating coil 234. The conductor 246 is connectedthrough the normally open contacts 248 of the control relay 2I4, aconductor 248, and a conductor 250 to the output conductor 23I.

Iii)

The sensitive relay 236 is provided with rela- 35 tively stationarycontacts 251 and 252, and a movable contact arm 253 normally inengagement with the contact 252. The stationary contact 251 is connectedto a conductor 254 in turn connected to the conductor 216.

The operating coil 255 of the control relay 214 has one of its terminalsconnected through one of the normally open contacts 256 of the controlrelay 214 to a conductor 251, normally closed contacts 253 and 252 ofthe sensitive relay 235, a conductor 258 in turn connected to theintermediate tap 225 of the transformer 226; and has the other of itsterminals connected through a conductor 259, normally closedcontacts 266of-a reset relay 261 and a conductor 262 to the conductor 245. Y

The duration of time that the switch 268 is maintained open may becontrolled by means herein identified as "off timing means for thereason that they determine the duration of. the "off period, that is,the period between successive application of current to the load 266,and comprise an output conductor 265 connected to the output conductor233 and thus to the rectifier 221. The output conductors 265 and 231supply unidirectional current to the operating coil 266 of a sensitiverelay 261 connected in series with a, neon tube 268.

A condenser 26!! is connected to the output conductors 231 and 265 inshunt with the sensitive relay coil 266 and the neon tube 268. Theresistance 236 is also shunted across the output conductors 231 and 265.

Interposed in the output conductor 266 is a a variable resistance 216and the normally closed 214 of the reset relay 26l to the conductor 256in I turn connected to the output conductor 231.

The sensitive relay 2611s provided with a relatively stationary contact215 and a movable contact arm 216 which is connected to the conductor264.

The operating coil 211 of the reset relay 26 I has one of its terminalsconnected through a conductor. 218 to the stationary contact 215 01 thesensi- 'tive relay 261, and has the other oflits terminals connected tothe conductor 262.

Interposed in the output'conductor 265 is a selector switch 213.whichperforms the same functions as described in connection with these-.

lector switch 186 inFig. 2. i I

In operation, assume it is desired to have repeat operation, that isalternate'operation of the "on timing means and of the off timing"means, the selector switch 216 is placed in its repeat position.

The push-button 211 is closed to complete an: energizing circuit tor theoperating coil 216 of the switch 268, from the supply line 262, throughconductor 216, push-button211, conductor 216,

normally closed contacts 213 of the control relay 214, conductor 212,operating coil 216, and the conductor 211 to the supply line 263.Energization of the operating coil 216 closes the switch 268 to permitcurrent flow through theprimary winding 213 of the transformer 226,toithe electrodes 266 and 261m begin the application of current1'.othe1oad26 6.'v I

l in

Closure of the push-button 211 also energizes the operating coil 242 ofthe relay 241 to close the contacts 246 and complete the circuits to thecondenser 231 and the neon tube 236.

The transformer 226 operates as a series transformer and a voltage isinduced in the secondary winding 221 from the primary winding 219. Thevoltage delivered by the secondary winding 221 is rectified by therectifier 221 providing unidirectional current tothecondenser 231. Thecondenser 231 accumulates a charge until a predetermined voltage isreached, at which voltage the neon tube 236 becomes conducting andpermits discharge of the charge accumulated in the condenser 231.

The operating coil 234 of the sensitive relay 235 is energized when theneon tube 236 becomes conducting, and is maintained energized for only ashort time to move the contact arm 253 into engagement with thestationary contact 251. Clo-v sure of the contacts 251 and 253 of thesensitive relay 235 completes an energizing circuit for the operatingcoil 255 of the control relay 214 from the supply line 262, throughconductor 216, pushbutton 211, conductor 254 contacts 251 and 253 of thesensitive relay 235, conductor 251, operating coil 255 of the controlrelay 214, conductor 253, normally closed contacts 266 of the resetrelay 261 and conductors 262 and 245 to the supply line 263.Energization of the operating coil 255 of the control relay 214 opensthe contacts 213 and closes the contacts 256 and 248 of the controlrelay 214. v

Opening of the contacts 213 de-energizes the operating coil 216 of theswitch 268, permitting the spring 263 to open the switch 268 whichinterrupts flow of current in the work-circuit through the primarywinding 213 and to the load 266, to thereby terminate the applicationofcurrent to the load 266. Opening of the contacts 213 also de-energizesthe operating; coil 242 of the relay 241, which then opens its contacts246 to interrupt flow of current to the condenser 231,

and closes its contacts21l to complete the circult of theoutputconductor 265 to the condenser 263 and sensitive relay 261.

At the same time closure of the contacts 246 of the control relay 214completes a shunt circuit from the output conductor 233 through aportion of the operating coil 234 of the sensitive relay 235, theconductor 246, contacts 248, and the conductors 249 and 256 to theoutput conductor 231.

The condenser 231 discharges through the foregoing/shunt circuit andmaintains'the tapped portion of the, operating coil 234, included in theshunt circuit, energized for a sufllcient'length of 256 of the controlrelay 214 are closed to complete a circuit to the transformer 226 tosupply the latter with .current from the supply line 262,

through conductors 216 and 216, contacts 256 o! the control relay 214,conductor 261, conductor m, the Winding :21 of-the transformer 226, andconductor 211 to the supply line 263. 75

' tacts 2.63 'and 262 oi the sensitive relay 235', con r The transformer228 now operates as an auto transformer and furnishes alternatingcurrent to the rectifier 227 which provides unidirectional current tothe condenser 269 through the output conductor and the closed contactsill of the reiay 2st. lhe condenser 269 accumulates a charge until apredetermined voltage is reached, at which voltage the neon tube 288becomes conducting and permits discharge of the charge accumulated inthe condenser 2E9.

The operating coil 265 of the sensitive relay 251 is energized when theneon tube 288 becomes conducting and is maintained energized for a shorttime to move the contact arm 2T6 intoengagement with the stationarycontact 215. Closure of the contacts 255 and 275 of the sensitive relay2E; completes an energizing circuit for: the operating coil ill? of thereset relay 266 from the supply line 262 through conductor 2E6,push-button Ell, conductor 255-, contacts 2H: and 215 of the sensitiverelay 261T, conductor M8, operating coil 2?? of the reset relay 26!, andconductors 262 and to the supply line 2133. Energization of theoperating coil ill of the reset relay 26l opens the contacts 2653 andcloses the contacts 276 of the reset relay iii-l.

Opening of the contacts 2% de-energizes the operating coil 255 of thecontrol" relay 2M, to open the contacts and to close the contacts Gun,

of the control relay 2. Closure of the contacts Zifi efiectsenergization of the operating coil 2 l which closes the switch 208 tosupply current to the primary winding 2w of the transformer 229 whichnow operates as a series transformer, to again supply current to theelectrodes and 2M and to the load Zllt.

At the same time closing of the contacts 2M of the reset relay 2G3completes a shunt circuit from the output conductor 265 through aportion or" the operating coil 2% of the sensitive relay 2ST, conductorEl-2, contacts 214, and conductor 250 to the output conductor 23L Thecondenser 26S discharges through the foregoing shunt circuit andmaintains the tapped portion of the operating coil 26%, included in theshunt circuit, energized for a sufiicient length of time to hold thesensitive relay contacts 215 and closed for a short time after resetrelay contacts 266 have opened. Maintaining thesensitive relay contacts275 and 2l6'closed for this short timeand reset relay contacts 260 open,insures i suiiicient de-cnergiaation of the control relay coil 2 5 todefinitely open the contacts 256 and to close the contacts 2l3. Afterclosure of the control relay contacts M3 the discharge from thecondenser 268 is too weak to hold the sensitive relay contacts H5 and276 closed, and accordingly contacts 275 and 216 open to break thecircuit to the operate to supply current to the load 200. l

In this embodiment I have provided means for automatically varying theduration of the period during which current flows to the load 20!. Theduration of the current flow period being greater for small currentspassing through the load 200, and less for large'currents passingthrough the load 206, that is, the duration of current flow period isautomatically determined and varied by the magnitude of the currentflowing through the load 2fl0.

The duration of the current flow period may be varied by varying theresistance 239, by varying the capacity of the condenser 23!, and byvarying the number of or characteristics of the neon tube 236.

.The current range of the transformer 220, when acting as a seriestransformer, may be altered by varying the resistance 230. Increasingthe resistance 230 increases the magnitude of the voltage in thesecondary winding 2 and thus the voltage furnished to the condenser 237,and causes the condenser 23! to more rapidly accumulate the voltagerequired to operate the neon tube 236, and decrease the duration ofoperation of the "on timing means and the duration of current flow inthe work-circuit.

The duration of the off period is dependent upon the magnitude of thevoltage supplied to and furnished by the transformer 22!), when it actsas an auto-transformer. The duration of the oil period may be altered byvarying the resistance 210, by varying the capacity of the condenser269, and by varying the number of or characteristics of the neon tube268.

It will be noted that in this embodiment I employ but one transformerwhich actsas a series transformer during the flow of current to the load200 and as an auto transformer during the oft period between successiveapplications 01 current to the load 209; and that I employ but onerectifying tube.

In Figures 2 and 3 I have omitted the pressure switch 6 and the controlvalve 9, and other parts of a spot welding machine as shown in Figure 1,but it will be understood that these omitted elements may be employed inFigures 2 and 3. The timing means need not be supplied with current fromthe same source of supply as the work-circuit. For example, the outputconductors 81 and 88 in Fig. 1 can be connected to a separate source ofeither alternating current or direct current, and when connected to asource of direct current supply the transformer 16 andv the rectifyingtube 8 can be eliminated. The output conductors H2 and I'll) of Fig. 2and the output conductors MI and 265 of Fig. 3 can be connected toseparate sources of either alternating current or direct current supply.

In Fig. l, I described my invention as applied to a spot weldingmachine, but'it is obvious, as shown in Figures 2 and 3, that myinvention is also applicable wherever the quantity of electricity to besupplied by a circuit is to be maintained approximately constant, andthe duration of time particularly pointed out or suggested herein, and

that the embodiments may he obviously changed and modified withoutdeparting from the spirit of my invention or sacrificing the advantagesthereof. It will be understood by those skilled in the art that thedisclosures herein are illustrative only and that my invention is notlimited thereto.

Having thus described my invention, I claim: I 1. Apparatus for timingthe periods during which a work-circuit is closed and open, comprisingzon-timing means for controlling the duration of the closed period; andoft-timing means for controlling the duration oi the open period betweensuccessive closed periods; the duration of one of. said periods beingdependent upon the magnitude of the voltage applied to one of saidtiming means, said one period being greater for small voltages appliedto said one timing means and less for large voltages; said one timingmeans including means for causing termination of said one period and foreffecting initial operation oi the other of said timing means.

2. Apparatus for timing the periods during which a work-circuit isclosed and open, comprising: on-timing means for controlling theduration of the closed period dependent upon the magnitude of thevoltage applied to said on-timing means, said closed'period beinggreater for small voltages applied to said on-timing means and less forhigher voltages; and oil-timing means for controlling the duration ofthe open period between successive closed periods dependent upon thevoltage applied to said off-timing means, said open period being greaterfor small voltages applied to said oft-timing means and less for highervoltages; said on-timing means including means for causing terminationof said closed period and for effecting initial operation of saidoff-timing means; and said off-timing means including means for'causingtermination of said open period and for effecting initial operation ofsaid on-timing means.

3. Apparatus .ior timing the periods during which a work-circuit isclosed and open, comprising: on-timing means for controlling theduration of the closed period dependent upon the value of the currentflowing in said work-circuit, said closed period being greater for smallcurrents through said work-circuit and less for larger currents; andoil-timing means for controlling the duration oiithe open period betweensuccessive closed periods; said on-timing means including means forcausing termination of said closed period and effecting initialoperation of said oft-timing means.

,4. Apparatus for timing the periods during which a work-circuit isclosed and open, comprising: on-timing means for controlling theduration of the closed period dependent upon the value of the currentflowingin said work-circuit. said closed period'being greater for smallcurrents through said work-circuit and less for large currents; andoil-timing means for controlling the duration of theopen period betweensuccessive closed periods dependent upon the voltage applied to saidoil-timing means, said open period being greater for small voltagesappliedto said off-timing means and less for high voltages; saidon-timing means including means for causing termination of said closedperiod and efi'ecting initial operation of said oil-timing means; andsaid oil-timing means including'means for'caus ing terminationio! saidopen period and effecting initial operation of said on-timing means.

5. Apparatus-tor timing the periods during which a work-circuit isclosed and open, comprising: on-timing means for controlling theduration of the closed period; off-timing means for.

controlling the duration of the open period between successive closedperiods; induction means for furnishing current to said on-timing meansand to'said oil-timing means; and means operable to alternately connectsaid on-timing means and said oil-timing means to said induction meansto effect alternate operations of said ontiming means and of saidoff-timing means.

6. Apparatus for timing the periods during which a work-circuit isclosed and open, comprising: on-timi'ng means for controlling theduration of the closed period; -off-timing means for controlling theduration of the open period between successive closed periods; powersupply means; switching means operable to alternately connect saidon-timing means and said oil-timing means to said power supply means toeffect alternate operation of said on-timing means and of saidoff-timing means, said switching means being rendered operative by eachof the timing means off-timing means; and means operable to alter-'nately connect said on-timing means to said induction means when actingas a series transformer and said oil-timing means to said inductionmeanswhen acting as an-auto-transformer, and to effect alternateoperations of said ontiming means and of said oil-timing means.

8. Apparatus for timing the periods during which a work-circuit isclosed and open, comprising: on-timing means for controlling theduration of the closed period; oil-timing means for controlling theduration of the open period between successive closed periods; one ofsaid timing means including means responsive to a. predeterminedelectro-motive-force for causing termination of its respective period,and including means for altering the value of the electromotive-forceapplied to said one timing means to said predeterminedelectro-motive-force, as required .to effect operation of saidresponsive means; and means operable to alternately connect saidon-ti'ming means and said oif-timing means to a source of electriccurrent to effect alternate operation of said on-timing means and ofsaid off-timing means.

9. Apparatus for controlling flow of current to a work-circuit,comprising: control relay means operable to disconnect said work-circuit'from a source of power supply; relay means having an operating coil andcontacts for effecting operation of said control relay means uponenergize,

tion of said operating coil; condenser means;'

. 10. Apparatus for controlling flow of current in a circuit,comprising: relay means having an operating coil; condenser means; meansforming one discharge path for said condenser means to energize saidoperating coil; and means including a portion of said operating vcoilfor forming another discharge path for said condenser means to energizesaid operating coil.

11. Apparatus for controlling iiow of current in a circuit, comprising:relay means having an operating coil; normally non-conducting meansrendered conducting at a predetermined voltage to complete an energizingcircuit for said operating coil; condenser means for renderingconducting said normally non-conducting means; means, including saidnormally non-conducting means, for forming one discharge path for saidcondenser means to energize said operating coil; and means, including aportion of said operating coil, forming another discharge path for saidcondenser means and to energize said operating coil.

12. Apparatus for controlling flow of current in a circuit, comprising:control relay means operable to control the current flow to saidcircuit; relay means having an operating coil and con tacts foreffecting operation of said control relay means upon energization ofsaid operating coil;

.condenser means; means forming one discharge path for said condensermeans to energize said operating coil and operate said contacts tooperate said control relay means; and means including a portion of saidoperating coil for forming another discharge path for said condensermeans to maintain said coil portion energized and said contacts in saidoperative position until said control relay means have definitelycompleted their control operation.

13. Apparatus for controlling flow of current in a work-circuit,comprising: timing means for controlling the duration of current flow tosaid work-circuit; a circuit for said timing means; transformer meansfor furnishing voltage to said timing means circuit; and resistancemeans shunted across at least a portion of said transformer means foraltering the voltage furnished by said transformer means to said timingmeans circuit, whereby increasing said resistance means increases thevoltage in said timing means circuit to decrease the duration of currentflow in said work-circuit.

14. Apparatus for controlling flow of current in a work-circuit,comprising: timing means for controlling the duration of current flow tosaid work-circuit; a circuit for said timing means; transformer meanshaving a primary winding in said work-circuit and a secondary windingfor furnishing voltage of magnitudes to said timing means circuitdepending upon the value of the current in said primary winding; andresistance means shunted across at least a portion of said secondarywinding for altering the voltage furnished by said secondary winding tosaid timing means circuit, whereby increasing said resistance meansincreases the voltage in said timing means circuit to decrease theduration of current flow in said work-circuit.

15. Spot welding apparatus comprising, in combination, a pair ofrelatively movable welding electrodes for engaging work, means formoving said electrodes into engagement with the work under pressure,means for applying welding current to said electrodes for apredetermined-time interval after a predetermined pressure is applied tothe work, and means for preventing the reapplication of pressure to thework for a predetermined time interval.

16. Spot welding apparatus comprising, in combination, a pair ofrelatively movable welding electrodes for engaging work, means formoving said electrodes into engagement with the work under pressure,means for applying welding current to said electrodes for apredetermined time interval, and means for preventing the re--application of pressure to the work for a predetermined time interval.

17. Spot, welding apparatus comprising, in combination, a pair ofrelatively movable welding electrodes for engaging work, means formoving said electrodes into engagement with the work under pressure,manually-operable means for initiating the functioning of said means,means for applying welding current to the work for a predetermined timeinterval, and means for preventing the reapplication of pressure to thework for a predetermined time interval after the expirationof saidfirst-mentioned time interval with said manual means in the operatedposition.

18. Spot welding apparatus comprising, in combination, a pair'ofrelatively movable welding electrodes for engaging work, means formoving said electrodes into engagement with the work under pressure,manually-operable means for initiating the functioning of said means,means for applying welding current to said welding electrodes and workfor a predetermined time interval after a predetermined pressure isapplied to the work, and means for preventing the reapplication ofpressure to thework for a predetermined time interval after theexpiration of said first-mentioned time interval with said manual meansin the operated position.

19. Spot welding apparatus comprising, in combination, fixed and movablewelding electrodes disposed to engage opposite sides of work i to bewelded, means for causing the movable electrode to engage the work underpressure, means for applying welding current to said electrodes andthrough the work for a predetermined time interval, means for relievingthe pressure applied to said electrodes after the expiration of saidtime interval, and means for preventing the reapplication of pressure tosaid electrodes for a predetermined time interval.

20. Spot welding apparatus comprising, in combination, fixed and movablewelding electrodes disposed to engage opposite sides of work to bewelded, means for causing the movable electrode to engage the work underpressure,

means for applying welding current to said electrodes and through thework for a predetermined time interval after a predetermined pres-' sureis applied to the work, means for relieving the pressure applied to saidelectrodes after the expiration of said time interval, and means forpreventing the reapplication of pressure to said electrodes for apredetermined time interval.

21. Spot welding apparatus comprising, in combination, a pair ofrelatively movable welding electrodes disposed to oppositely engage workto be welded, fluid pressure means operable to cause the electrodesto-engage the work, circuit means for applying welding current to saidwelding electrodes and through the work for a predetermined timeinterval, pressure responsive means for initiating the functioning orsaid circuit means on application of a predetermined pressure t4) thework, means for relieving the pressure applied by said pressure means tothe work 'after'the expiration of said time interval. and means forpreventing the reapplication of pressure to the work for a predeterminedtime interval.

22. Spot welding apparatus comprising, in'

Till

combination, fixed and movable welding elec- -15 which a work circuit isclosed and open and comable means ior initiating the functioning of saidpressuremeans, a current source, circuit means for connecting thewelding electrodes to the current source for a predetermined timeinterval,-

pressure responsive means for initiating the functioning of "saidcircuit means on application of a predetermined pressure to the work,means for relieving the pressure applied by said pressure means to thework after the expiration of said time interval, and means forpreventing the reapplication of pressure to the work for a predeterminedtime interval with said manual means in the operated position.

23.,Apparatus for timing the periods during which a work circuit isclosed and open, comprise ing a means for on-timing to control theduration' 01' the closed period, and another means for oif timingtocontrol the duration o the open period 'between successive closedperiods, each of said timing means including means for effecting initialoperation of the other of said timing means .upon termination of its owntiming period; and means to vary the duration of one of said periodsinversely with variations of the voltage applied to the timing meanswhich conperiod independently of the duration of the timing periodof theother timing means.

25. Apparatus for timing the period during prising on-timing means forcontrolling the duration of the closed period, said closed period beinga function of the voltage applied to said trolling the duration of theopen period between successive closed periods, said open period being afunction of, said voltage applied to said otttiming means, saidon-timing means including means for causing termination of saidclosedperiod and for eflecting initialoperation of said off-timing, means, andsaid ofl-timing means including means for causing termination of saidopen period and for eflecting initial operation of said on-timing means.

-26.-Apparatus for timing the period during' work circuit, said closedperiod being greater for small currents through said ,work circuit andless for large currents, and an off-timing means for controlling theduration of the open period between successive closed periods; said openperiod being a function of voltage applied to said oiftiming means, saidon-timing means including means for causing termination of said closedperiod and effecting initial operation of said oiltiming means, and saidoff-timing means including meansfor causing termination of said openperiod and efiecting initial operation of saidontiming means.

27. In a spot welding device including electrodes movable, priomto theinitiation of welding current, into contact with work pieces to bewelded, and to be separated from the work pieces after the cessation ofthe welding current, apparatus for timing the intervals during which thespot welding device is welding and not welding, comprising a means foron-timing to control the duration of the welding interval, and anothermeans for off-timing to control the duration of the period during whichthe electrodes are separated from the work pieces, and the part of thenon-(welding interval coextensive therewith, said oil-timing means meansafter termination of its own timing interval, said oil-timing meansincluding meansresponsive to a predetermined electromotive force forcausing termination of its said timing interval.

DAVID C. WRIGHT.

including means for initiating operation of the on-timing

